The present invention relates to optical sensors, and especially to optical code readers, and to a method for operating such sensors, which involves receiving reflected light with a light receptor, generating a picture therewith, reading the picture (code) and compressing at least some of the pictures with a picture compression algorithm.
Code readers read codes, such as one-dimensional bar codes or two-dimensional matrix codes, and they operate according to a variety of principles. Code readers which employ the scanner principle read the code by scanning a light beam over the object in question, for example a label carrying a bar code. Light reflected or returned by the object is received by a light receptor and converted into electronic signals. Bar code information is derived from amplitude information of the electric signals.
Two-dimensional codes are typically read with code readers that operate on the camera principle. The object in question is illuminated with surface lighting or line-like light fields and results in light that is reflected or returned by the object and received by a one- or two-dimensional receiver array, for example a CCD or CMOS line or matrix sensor. By making use of the amplitude differences of the received pixels, the code and therefrom code information can be derived.
U.S. Pat. No. 5,703,349 discloses a portable code reader which compresses received pictures prior to further processing them to facilitate, for example, their wireless transmission.
Depending on the code quality, the degree of contrast the code contains, as well as any damage or soiling to which the code was subjected, can lead to error readings. Such incorrectly read data is typically immediately discarded because it is not useful. However, without the erroneously read data it is difficult to diagnose what led to the errors in the first place.